Pentanediamine (pentanediamine mentioned in the present invention refers to 1,5-pentanediamine, alias 1,5-diaminopentane, pentamethylene diamine, cadaverine) is an important chemical intermediate, mainly used as a monomer for preparing polymers such as polyamides, an organic synthesis intermediate, and an epoxy resin curing agent, and also used for biological research. Nylons, which are obtained by polymerization of 1,5-pentanediamine, can be used in many aspects of daily production and life, such as electronic appliances, mechanical equipment, and automobile parts.
Industrially, the process for preparing 1,5-pentanediamine is as follows: a solution of 1,5-pentanediamine salt is obtained by fermentation or enzymatic conversion process; the salt solution is treated by adding alkali, extraction and evaporation and the like to obtain an aqueous solution of 1,5-pentanediamine, followed by distillation to give 1,5-pentanediamine. In the preparation of 1,5-pentanediamine, in addition to 1,5-pentanediamine, by-products containing an unsaturated bond, such as 2,3,4,5-tetrahydropyridine (THP), are also produced.
In the process for preparing nylons with 1,5-pentanediamine as the starting material, the presence of the unsaturated by-product THP would affect the subsequent polymerization of 1,5-pentanediamine, thereby reducing the product quality of the polymer such as nylon 56. In particular, THP would cause the discoloration or branching of the polymer. Thus, reducing the amount of impurity THP in the 1,5-pentanediamine product can avoid the discoloration of the polymer and is critical to the improvement of the quality of the polymer product.
In the prior art relating to the removal and effective control of impurity THP, as described in EP 26684867 of Mitsui Chemicals, the fatty alcohols having 4 to 7 of carbon atoms are used as extractant to extract 1,5-pentanediamine from a fermentation broth, which can effectively reduce the THP content in the 1,5-pentanediamine products. Taking n-butanol as an example, the extraction rate thereof is 91.6%, the content of THP in the product is 0.1 wt %; and when using isobutanol as solvent, the extraction rate is 86.0%, the content of the impurity THP in the product is 0.1 wt %, and when using chloroform as extractant, the extraction rate is only 61.7%, the content of the impurity THP in the product is 0.6 wt %. Although the extraction by fatty alcohol with 4 to 7 of carbon atoms may obtain a better result than using chloroform as extractant, such extraction still has some defects such as relatively low extraction rate, difficulty in the separation of the layers, and high energy consumption in recovery of the extractant, and is not suitable for large-scale production.
As described in CN102449029 of TORAY INDUSTRIES, INC., the polyamide resins obtained by polymerizing 1,5-pentanediamine having a total content of 0.1% of THP and piperidine have better performance and quality, wherein the extraction process of the amine raw material is carried out by using chloroform as extractant and further distillation under reduced pressure to obtain 1,5-pentanediamine with the total content of impurities THP and piperidine less than 0.1%. Clearly, the extraction rate of chloroform is relatively low, as a result, a large amount of 1,5-pentanediamine present in the aqueous phase is not effectively extracted, thus the product yield is low, and the loss is significant.
Therefore, how to remove and effectively control the content of impurity THP in 1,5-pentanediamine products has become a key factor in controlling the quality of 1,5-pentanediamine products and a “bottle neck” for improving the quality of nylon products prepared by 1,5-pentanediamine.